Such a method is known from EP 478 051. This document discloses the continuous manufacture of a flat substrate from a fibre-reinforced matrix, which process comprises the use of at least two moving layers of parallel, rectilinearly extending reinforcing fibres not bonded in the fore of a woven fabric (UD fibres), providing said UD fibres, which are positioned in at least two crossing directions, with matrix material, and passing them through a laminating zone, for instance a double belt press, to fore a cross-ply laminate. By this process laminates may be obtained which are pre-eminently suitable as PWB substrate on account of, int. al., their good surface area quality, their comparatively low linear thermal coefficient of expansion (TCE) in the x and y directions, the option of incorporating a high content of fibres, and their favourable dimensional stability.
A drawback to the known method is that the laying of the fibres in two directions and their being provided with matrix material before or after said laying, prior to the curing of the matrix material provided with fibres, requires a comparatively complex apparatus. Another disadvantage is that in order to retain the desired orientation, generally 90.degree., the UD fibres must be kept under tension throughout the entire process. Also, it is desired to increase the process's yield of material.
Another method of manufacturing a UD layer-reinforced composite laminate, which likewise is intended to be used as a PWB substrate, is known from U.S. Pat. No. 4,943,334. In this process reinforcing filaments are wound about a square flat mandrel in several layers crossing at an angle of 90.degree., with the filaments being provided with curable matrix material by means of injection and/or impregnation. The matrix, which in consequence contains cross-wise applied UD fibre layers, is then cured. An advantage of this method is the low coefficient of expansion attainable in the thus manufactured substrate. A possible drawback to this method resides in the high interlaminar stresses extant in the manufactured product as a result of the anisotropy of the layers of which the laminate is composed. There is a risk of these stresses leading to delamination. The high production costs are another major disadvantage, and there is also the fact that a comparatively large quantity of material is wasted at the edges.
From U.S. Pat No. 4,420,359 it is known to manufacture reinforced plastics laminates by laminating one or more layers of a resin-impregnated, fibre-containing plastics material with rigid flat panels. The specification provides a description of an apparatus for laminating in which use is made of two continuous belts between which the lamination process is carried out.
At issue in U.S. Pat. No. 4,659,425 is the manufacture of PWBs by coating the surface of a metal foil with a thermosetting resin, contacting the thus coated metal foil with a reinforcing cloth, e.g. a glass fabric, to form a foil/cloth assembly, and then passing such foil/cloth assemblies through a double belt press in order to obtain a laminate.
The use of a double belt press in manufacturing PWB laminates and multi-layer PWBs is also known as such from EP 120 192, EP 203 368, EP 215 392, and EP 327 838. However, these publications do not make mention of UD layer-reinforced composites.
Composite materials for PWBs in which individual crosswise positioned UD layers are employed are known from U.S. Pat. No. 4,814,945. This publication relates to a resin reinforced with parallel fibres of aramid being used as a PWB substrate. Several resin layers heated to a semi-cured or B stage and so UD-reinforced are placed one on top of the other and then cured. A drawback to the use of resin layers in the B stage is that, on account of the flow which occurs during lamination, the tension, and hence the orientation of the UD layers cannot be adequately controlled, causing a deficiency in flatness. Particularly in the case of PWB laminates a deficiency in flatness is a disadvantage. A further drawback associated with the use of resin layers in the B stage has to do with the problems involved in storing such a still reactive material.
The background art further includes:
U.S. Pat. No. 4,609,586, from which a cross-ply laminate for PWBs is also known. This, however, is a carbon fibre-reinforced metal matrix which is not utilised as the actual substrate (in this case a conventional glass fabric/epoxy composite), but as an additional supporting component.
U.S. Pat No. 3,150,026 discloses an apparatus for producing a non-woven, plastic reinforced fabric, wherein parallel fibrous warp strands are advanced along a support, consecutive lengths of parallel weft strands are placed onto the advancing band of warp strands, and wherein downstream of the support a bonding resin is applied to the warp and weft strands and cured.
U.S. Pat. No. 4,186,044 discloses a device for continuously pressurizing and curing resin impregnated multilayered reinforcements into an elongated laminated composite structure.
In FR 2 330 530 a reinforced belt is produced by advancing two parallel rolls of longitudinal reinforcement material, applying transversal reinforcement material to form a continuous belt of bidirectional reinforcement material, providing a bonding agent, and bonding the reinforcement.
FR 2,333,638 discloses the manufacture of rubber transport belts involving the extrusion of reinforced belts, cutting similarly manufactured belt material into panels, and transversally providing the produced belts with said panels, followed by pressing and vulcanizing.
The invention has for its object to provide a simple, comparatively inexpensive method of manufacturing UD-reinforced composites without the drawbacks associated with the prior art discussed hereinbefore. Notably, it is envisaged to manufacture UD-reinforced composites which are pre-eminently suited to be used as a PWB substrate.